1. Field of Invention
The present invention relates to a method of manufacturing a liquid crystal display panel. More particularly, the present invention relates to a method of curing a seal and a method of manufacturing a liquid crystal panel by using the same.
2. Description of Related Art
Following the rapid advance in high-tech electronics products, video and especially digital video and imaging devices have become common electrical appliances in our offices and homes. Among the video and imaging devices, displays are very important and indispensable devices for showing data interactively. Through a display device, a user can read out important information or use the information to control a particular system.
To fit into our current style of living, the video or imaging products are becoming slimmer and lighter. Although a conventional cathode ray tube (CRT) can still provide clear images at a relatively low cost, it is gradually being phased out because of bulkiness and relatively large power consumption. With the great advances in opto-electric technologies and semiconductor fabrication techniques in recent years, flat panel displays such as the liquid crystal displays have become the most common display product. The advantages of the liquid crystal displays include a low operating voltage and a radiation free operation. In addition, the liquid crystal panel not only has a weight considerably less than a CRT, but also occupies a volume considerably less than a CRT. Together with some other flat panel displays such as the plasma displays and the electroluminance displays, some researchers have forecast the increasing use of liquid crystal displays in the 21st century.
One major type of liquid crystal display is the so-called thin film transistor (TFT) liquid crystal display (LCD). The TFT-LCD comprises a thin film transistor array substrate, a color-filtering array substrate and some liquid crystals as shown in FIGS. 1A and 1B.
FIG. 1A is a top view showing the layout of the liquid crystal panel of a conventional thin film transistor liquid crystal display. FIG. 1B is a cross-sectional view along line I–I′ of FIG. 1A. As shown in FIGS. 1A and 1B, the liquid crystal panel 100 of the thin film transistor liquid crystal display (TFT-LCD) comprises a thin film transistor array substrate 102, a color-filtering array substrate 104 and some liquid crystals 106. The liquid crystals 106 fill up the space between the thin film transistor array substrate 102 and the color-filtering array substrate 104. To prevent the liquid crystals 106 from leaking away, a seal 108 is set up around the edges of the overlapping region between the thin film transistor array substrate 102 and the color-filtering array substrate 104.
At present, there are two major types of seals 108, the thermal curing type and the ultraviolet (UV) curing type. To fabricate a liquid crystal display panel using the thermal curing seal, thermal curing seal is smeared around the edges of the color-filtering array substrate 104. The color-filtering array substrate 104 is aligned over the thin film transistor array substrate 102 and the two are pressed together so that they are joined through the seal 108. Thereafter, a jig press or a hot press is used to cure the seal 108 in a thermal curing process. After the seal 108 is fully solidified, liquid crystals 106 are injected into the space between the thin film transistor array substrate 102 and the color-filtering array substrate 104 and bounded by the solidified seal 108. Afterwards, the injection hole is sealed with UV plastic material. Similarly, to fabricate a liquid crystal display panel using an UV seal, UV sealing material is smeared around the edges of the color-filtering array substrate 104. The color-filtering array substrate 104 is aligned over the thin film transistor array substrate 102 and the two are pressed together so that they are joined through the UV seal 108. Thereafter, the UV seal 108 is irradiated with UV light to cure the UV seal. In the conventional UV exposure method, the UV light penetrates through the panel. After the UV curing process, liquid crystals 106 are injected into the space between the thin film transistor array substrate 102 and the color-filtering array substrate 104 and bounded by the solidified seal 108. Afterwards, the injection hole is sealed with UV plastic material.
Due to the material limitations of sealing material and the reliability of the panel, conventional thin film transistor liquid crystal display opts for the thermal curing type of seals. However, the thermal curing type of seal has a long curing period and upper/lower substrate alignment problem. Moreover, the curing period is too long for applying the new one-drop filling method. The so-called one-drop filling method includes dropping liquid crystals directly into the region bounded by the UV seal 108 after the UV seal is applied to the edges of the thin film transistor array substrate 102. Due to the long curing period of the thermal curing seal and the possible contamination of the liquid crystals during the curing process, thermal curing seal is unsuitable for carrying through with the one-drop filling process.
Therefore, the UV seal is almost exclusively deployed when the one-drop filling process is used. However, the conventional UV exposure method uses a beam of penetrating UV light to irradiate the UV seal so that the liquid crystals adjacent to the UV seal may also be irradiated. Since liquid crystals can absorb ultraviolet light within a definite wavelength range (for example, between 100 to 400 nm), the penetrating UV beam may damage some of the liquid crystal molecules leading to the production of a defective display screen. To prevent this from happening, either a UV beam having constituent wavelengths outside the absorption range of the liquid crystal molecules is used to cure the UV seal or the UV curing method as shown in FIG. 2 is used to cure the UV seal.
FIG. 2 is a magnified view of a portion of the area labeled 11 in FIG. 1B. As shown in FIG. 2, an additional mask 214 is formed over the liquid crystal layer 206 in the process of curing the seal 208 between the thin film transistor array substrate 202 and the color-filtering array substrate 204 to block the light from a UV source 212. Alternatively, the black matrix 210 and the color thin film within the color-filtering array substrate 204 are used as a mask to block the UV light 212.
There are two shortcomings resulting from the above, improved process. One is that it makes the process complicated and raises the cost owing to the additional mask. The other shortcoming is that when the black matrix and the color thin film within the color-filtering array substrate can not block ultraviolet light within a definite wavelength range, it is ineffective to use the black matrix and the color thin film within the color-filtering array substrate as a mask.
When the black matrix 210 is used to block UV light, a portion of the seal 208 may be shielded from UV light and prevented from a UV cure. Furthermore, if the black matrix 210 happens to block off all UV light heading for the UV seal 208, the conventional method of curing with penetrating UV light can no longer be applied.